1. Field of the Invention
The present invention relates generally to paint formulations and, more particularly, this invention relates to paint solutions and methods of preparing the same.
2. Description of Related Art
In the past, solvent based paints have generally out-performed latex paints whenever there has been a comparison of properties such as water resistance, abrasion resistance, resistance to moisture vapor transmission, adhesion to most surfaces, gloss quality, recoatability, and minimum application temperatures. Differences in the formulations of solvent based paints and latex paints, at least in part, account for the differences in the properties of the resulting paint films formed thereby.
In solvent based paints, there is an external phase consisting of a resin (or an oil) dissolved in a solvent and an internal phase consisting of a pigment dispersed to a finite particle size. Upon evaporation of the solvent, a film is left behind wherein the internal phase is completely encapsulated by the external phase which itself has flowed out to form a continuous, impermeable entity. A solvent based paint formulation may be such that the film resulting upon evaporation of the solvent cross-links (cures), at either ambient or elevated temperatures, with other materials in the external phase or with oxygen in the air to form larger molecules. In several systems, most notably vinyls and lacquers, the external phase does not "cure" but rather forms a film after the solvent, which had been used to solubilize the resin, has evaporated.
Solvent based paints, however, have several disadvantages. First, volatile organic solvents are costly and sometimes noxious and dangerous to use. Second, the viscosities of solvent based compositions vary significantly with the amount and molecular weight of the dissolved film former. Also, the application characteristics of these solution coatings often make it necessary to apply many coatings of these materials since they contain a low percentage of solids.
Generally, conventional latex paints include two phases, an external phase and an internal phase. The external phase is water in which additives, such as wetting agents (surfactants or emulsifiers), dispersants, cellulosic thickeners to control paint rheology and package stability, glycols to control application characteristics and temperature sensitivity, and bactericides to protect the paint from bacterial attack and putrefaction, are added. Film forming solvents, also known as coalescing agents, may also be added to the formulations. If the coalescing agents are miscible with water, they may be dissolved in the external phase, otherwise, they may be emulsified so as to become a part of the internal phase.
The internal phase of conventional latex paints contains pigment dispersed to finite particle size, latex particles which can never be solubilized and, in some cases, micelles of film forming solvent. Upon evaporation of the water, a relatively non-continuous film of particles of pigment and latex is left behind. The particles comprising this latex paint film are bound together and adhere to the surface to which the paint has been applied by means of the latex particles which are softened and made adherent by the addition of the film-forming solvent. The resulting softened latex particles are adherent to each other, to pigment particles and to the surface to which the latex paint is applied.
As is generally known in the art, unless heated to a sufficient temperature so as to melt the latex particles, conventional latex paint formulations which include film forming solvents result in latex paint films which are not as densely packed or as free from air pockets as those films resulting from solvent-based paints.
Alternatively, a latex paint may be prepared without including film forming solvents therein by preparing a relatively soft latex resin. Such a soft latex resin is very adherent, but this adhesiveness in turn creates problems. For example, soft latex resins generally have poor package stability and oftentimes result in permanently sticky films.
Also, the presence of dispersants and/or wetting agents in a paint formulation leave the film formed by that paint permanently sensitive to water and cleaning agents.
Thus, while known latex paint formulations generally avoid many of the aforementioned disadvantages of solvent based paints, they generally do not form tough, smooth, water-resistant coatings which adhere well to finished substrate surfaces.